Films made of thermoplastic resin containing light-reflecting pigment typified by powdery aluminum and white pigment such as titanium oxide or light-absorbing pigment such as carbon black added thereto have heretofore been used as a light-shielding material which is employed mainly as a covering material for greenhouses in the fields of agriculture and horticulture. Making a film containing a light-reflecting pigment such as powdery aluminum and white pigment have a light transmission reduced to a certain level or lower requires addition of a large amount of pigment. The addition of a large amount of pigment will cause problems, e.g. reduction in productivity such as breakage at stretching into a thin film and reduction in mechanical properties. Further, the films containing a light-absorbing pigment such as carbon black are problematic in that the films absorb the light in the daytime and release it as heat in the night to cause the temperature increase in houses.
A light-shielding material made of a thermoplastic resin film such as that mentioned above is so poor in durability that when it is employed alone as a covering material for a house, it is easily broken due to the force applied to the film during the work of spreading it as a house covering material or during the daily-conducted opening and closing work.
JP-A 11-333978 discloses a translucent heat-insulating sheet obtained by laminating an aluminum deposition film and a woven fabric made of flat yarns of high density polyethylene by sandwich lamination. However, the aluminum deposition film is not suitable for folding or the like during the opening and closing work as a house covering material and is problematic in that the aluminum deposition layer peels off.
JP-A 9-172883 discloses a light-shielding net obtained by weaving flat yarns with tape-like fiber lines, which were used as warps and wefts, produced by slitting a nonwoven fabric composed of synthetic resin filaments piled and bonded in high density and in random directions. JP-A 10-327684 discloses a light-shielding net comprising a net base fabric obtained by weaving flat yarns, onto one side of the net base fabric tape-like fiber lines produced by slitting a nonwoven fabric composed of synthetic resin filaments piled and bonded in high density and in random directions have been welded while being spaced apart from one another. However, films or tapes made of such light-reflecting nonwoven fabric are unsatisfactory in abrasion resistance and in strength. They are also defective in handlability at the time of opening, closing and folding because they are bulky. Moreover, they are polluted during their outside use by, for example, adhesion of dust or generation of moss caused by entrance of rain water, then their light reflectance easily decrease. In addition, such nonwoven fabric is more expensive than normal films.
The present invention was made in light of the problems mentioned above. The object of the present invention is to provide a light-shielding sheet which has a lightweight, a high strength and a superior durability and which inhibits the temperature increase caused by absorption of heat from sunlight.